Summary: The predominant proteins in the outer membranes of N. gonorrhoeae are trimeric porin proteins (protein I or PI). They are considered good vaccine candidates because porin protein is expressed by all strains, they are surface exposed, and, although antigenic variation exists between different strains, there is no phase variation during an infection as there is for both pilin and lipooligosaccharide (LOS). A model of these neisserial porin proteins predicts eight surface exposed loops. Regions of variability between serotypes in the genes coding for these proteins have been mapped and it is predicted that these variable region (VR) loops form the epitopes for both serotyping and induction of bactericidal antibodies. We have developed a genetic typing method that identifies VR sequences of the por gene of PIA and PIB strains of N. gonorrhoeae and utilized this method to type the por gene in samples from a variety of collections of strains (over 1000 samples recieved, including international collaborations). The results suggest that 1) in a group of temporally and geographically related strains there is a limited degree of variation in regions of the PI protein that are of suspected immunologic importance; 2) serovar typing cannot accurately identify porin VR similarities and differences between strains suggesting that a variable region specific typing system is preferable in studies designed to address questions about the antigenicity and protective potential of the PI gonococcal protein; 3) common por VR types persist in the population of strains circulating in a community over time and 4) the diversity of the porin protein in gonococcal isolates is due in large part to genetic mosaicism (from horizontal gentic exchange) and that the molecular diversity of individual variable regions is very limited. The por VR typing method provides specific information about individual variable regions of the Por (PI) protein and therefore may contributes to studies of structure/function, host immune responses, and transmission. For example, we studied 53 disseminated gonococcal disease (DGI)isolates and found a single PIA por type was present in 85% of the PIA strains. This por type has not been observed frequently among uncomplicated mucosal infections. Also, we have found that although genetic mosaicism is evident in the por gene, several non-adjacent variable regions do not appear to vary independantly suggesting that there may be structural or funtional effects that influence por diversity. We have adapted our method to allow typing of N. gonorrhoeae from non-culure based samples such as urine, cervical wicks and vaginal lavage, and will participate in a large study examining gonococcal transmission. The por VR typing method was developed primarily as a tool to allow us to characterize the PI protein of strains to allow for evaluation of specific immune responses to this outer membrane protein. We are now developing methods to examine serum and mucosal immune responses to the porin proteins following natural infection with Neisseria gonorrhoeae.